Sunday 6 August 2023

Dre-XT-Stück - exhaust rebuild (even better-er?)

During the engine rebuild it became rather apparent that the exhaust might be in need of "some" love too. 

So step one was to permanently weld the db-killer in place as previously it was only held in by one (semi-)seized bolt.

Whilst fixing stuff that worked before, I also got a TT600S stainless steel exhaust header.

The big benefit with one of these is that they have better flanges, which do not bend the exhaust studs. Unfortunately this also meant getting all the old ones out. Now call me a pessimist, but I installed all of them with copious amounts of copper-grease, so it was just a matter of double-nutting and winding them out.

Stock studs are M6x32mm. I, following some advice from the XT-Forum, installed M6x45mm studs. Those are too long and I later on replaced them with M6x40mm (stainless) studs later on.

The TT600 headers are too long by about 40-45mm. In my case (take that with a grain of salt as all exhaust bits on this XT are now homegrown), I had to cut off close to 50mm to get them to the right length...

... because it wouldn't clear the airbox, I cut off another 30mm. Guess what, it was now too short by about 30mm. Turns out, you have to undo the 3 bolts that hold on the airbox and then everything will fall into place nicely. Also high-frequency (120Hz, 33% on-time with a 15/70A split) creates absolutely stunning welds with no burn-through to the backside.

With that out of the way it was time to turn my attention to the actual muffler. For that I bought some 2" and 55mm perforated tube. The bigger diameter tube was meant to locate the thinner tube, which slides over a hump on the far-side of the muffler. This way the inner tube is free-floating and can expand and contract depending on how hot it gets.

Another benefit: trimming the inner tube to length is very straight-forward.

As all four nuts where missing previously and the last guy who "fixed" the exhaust used the nutserts to hold both the cap and outer body together... a proper bit of welding was due.

Probably the smartest trick for repacking exhausts I learned ages ago is to wrap the inner tube with some matt (or wool it works the same) and then tighten and wrap it with (paper-)masking tape. You end up with a VERY tightly packed exhaust. The masking tape will burn off and the packing will unfold a bit and fill the whole exhaust more evenly. This way it also lasts a lot longer.

It is a bit loud though, when freshly packed. 

By the time I had come home from my workshop (about 15 to 20kms later), the masking tape had burned off and the sharp bark has all but disappeared. I actually think at around 2000-2500 rpm it is now more quite than my (leaky) stock exhaust.

Just showing off the model number (this Arrow exhaust is so old, it sorts of predates E-numbers) and is stamped on the inside to make it easier to see where the marking is. (Without the need to remove any sidepanels.)

Also yes, it is a heavily modified item originally meant for a Honda XR600R.